1. Field of the Invention
The present invention relates to a video signal processor which determines a composite video signal or a component video signal as an input video signal, and more particularly, it relates to a video signal processor which can remove an image quality debasing component in a composite video signal and a component video signal to improve the image quality.
2. Description of the Related Art
As video signals to be input to an image display apparatus, there are a composite video signal, such as an NTSC signal or a PAL signal, in which a luminance (Y) signal is composed with a color (C) signal, and a component video signal in which a luminance signal is separated from a color signal or a color difference signal. When a composite video signal is determined as an input video signal, a luminance signal and a color signal must be accurately separated from each other or else a dot interference by which a color signal component is mixed in a luminance signal or a cross-color interference by which a luminance signal is mixed in a color signal occurs. Thus, in order to display a high-quality picture without such a dot interference or cross-color interference, a luminance signal and a color signal must be accurately separated from each other.
In order to accurately separate a luminance signal and a color signal from each other, a motion adaptive three-dimensional Y/C separation circuit utilizing a frame correlation is used. The motion adaptive three-dimensional Y/C separation circuit performs two-dimensional processing utilizing a line correlation with respect to a moving image portion and performs three-dimensional processing utilizing a frame correlation with respect to a static image portion, thereby separating a luminance signal and a color signal from each other.
FIG. 1 is a block diagram showing a schematic structure of a general video signal processor including a three-dimensional Y/C separation circuit, in which a composite video signal and a component video signal is determined as input video signals. In FIG. 1, a composite video signal is input to an input terminal 1, and a component video signal is input to an input terminal 2. The composite video signal is input to a motion adaptive three-dimensional Y/C separation circuit 3, and the three-dimensional Y/C separation circuit 3 performs three-dimensional Y/C separation by using a signal subjected to frame delay with a frame memory 4. Here, the three-dimensional Y/C separation circuit 3 and the frame memory 4 are very simplified and conceptually shown. A luminance signal Y and a color signal C output from the three-dimensional Y/C separation circuit 3 are input to a color demodulation circuit 5. The color demodulation circuit 5 color-demodulates the color signal C, converts it into a color difference signal CD, delays the luminance signal Y, performs time adjustment of the luminance signal Y and the color difference signal CD, and outputs them.
The luminance signal Y and the color difference signal CD output from the color demodulation circuit 5 are supplied to an output terminal 7 through a terminal a of a switch 6. The luminance signal Y and the color difference signal CD output from the output terminal 7 are supplied to another signal processing circuit which is not shown, and displayed in a display portion. Since the component video signal (the luminance signal Y and the color difference signal CD) input to the input terminal 2 does not have to be subjected to processing in the three-dimensional Y/C separation circuit 3 and the color demodulation circuit 5, it is supplied to the output terminal 7 through a terminal b of the switch 6. The switch 6 is switched by a non-illustrated control portion in such a manner that it selects the terminal a if the input video signal is the composite video signal and selects the terminal b if the input video signal is the component video signal.
Incidentally, as a known example which improves the image quality of the composite video signal, there is an example described in Japanese Patent Application Laid-open No.2003-70018.
A phase of a color signal in an NTSC signal or a PAL signal is rotated in a frame cycle. The phase is rotated 180° in one frame in case of the NTSC signal, and the phase is rotated 180° in two frames in case of the PAL signal. In order to detect a motion of an image, a calculation must be carried out by using frames in which color signals are in phase. In such a conventional structure as shown in FIG. 1, a motion of an image must be detected by using a current frame and a frame delayed for two frames in case of the NTSC signal, and a motion of an image must be detected by using a current frame and a frame delayed for four frames in case of the PAL signal. In the conventional video signal processor shown in FIG. 1, therefore, there is a problem that a detection error is apt to be generated in detection of a motion of an image.
On the other hand, the component video signal does not include a dot interference component or a cross-color interference component since it is essentially a signal in which a luminance signal is separated from a color difference signal, but the component video signal including a high-vision (HD) signal transmitted from a broadcasting station in digital broadcast or the like may be a signal obtained by up-converting a standard (SD) signal such as an NTSC signal or a signal obtained by being once converted into a composite video signal in a storing or editing process in the broadcasting station and being restored to the component video signal in some cases. Such a component video signal may aboundingly include dot interference components or cross-color interference components in some cases.
In the conventional video signal processor shown in FIG. 1, the three-dimensional processing cannot be performed with respect to the component video signal including a dot interference component or a cross-color interference component, there is a problem that the dot interference or the cross-color interference is generated. In the structure shown in FIG. 1, adding a circuit which also performs the three-dimensional processing with respect to the component video signal can remove the dot interference component or the cross-color interference component, but a circuit scale becomes large, which results in a great increase in cost.